Volumetric modulated arc therapy (VMAT) or arc therapy has been widely adopted in cancer radiotherapy. VMAT delivers radiation by rotating the gantry through one or more arcs. Compared with the conventional radiotherapy, VMAT can achieve highly conformal dose distributions with improved target volume coverage and cause less damage to normal tissues. Additionally, VMAT can reduce treatment delivery time compared with conventional radiotherapy, such as static field intensity modulated radiotherapy (IMRT).